DIY Network

Understanding Tomato Diseases

Expert tips on how to cope with tomato diseases in your vegetable garden.

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Tomatoes are a key crop to the summer veggie garden, so when disease hits your prized tomatoes, it can be devastating on your harvest. Here are some expert tips to keeping your tomato plants healthy and bountiful.

Select disease-resistant varieties of tomatoes for your vegetable garden. If you see the initials VFN on a tomato seed packet, it means that the variety is resistant to verticillium wilt, fusarium wilt and root knot nematodes. A T on the label means the variety is resistant to tobacco mosaic virus, which can be problem for tomatoes, especially if they're grown near tobacco. When choosing tomato plants in the nursery, avoid those with visible leaf spots.

How can you tell whether your tomato plant has a disease? Infected plants usually have poor color and are unproductive. Also look for brown or dying spots on the leaves. Wilted plants are an indicator of stress.

Nematodes
Nematodes are microscopic roundworms that feed on roots, interfering with the plant's ability to take up water or nutrients and causing stunted growth. Unfortunately, you can't tell for sure whether a plant is suffering from this disease without pulling it up and examining the roots. Nematode damage shows up as galls, or knots, on the roots.

To avoid the problem in future, don't grow tomatoes in the same location two years in a row. Grow a cover crop, such as rye, where tomatoes were planted to sweeten the soil by fixing nitrogen and improving soil tilth. You can also plant nematode-resistant varieties and plant marigolds -- which help eliminate nematodes -- in the tomato patch. If you use the crop rotation method, move your tomato plants 15' to 20' from the original site the following year.

Blight
When a tomato is infected by early blight, the leaves begin to die from the bottom of the plant, and the disease works its way up the plant. Early blight can show up at any time during the growing season but typically in periods of hot, wet weather, while late blight shows up later in the growing season and typically during periods of cool, wet weather. Late blight is not as common as early blight. Both show symptoms on the leaves and fruit. Fungicide sprays may be used to prevent these two diseases. Avoid blight on tomatoes by keeping the soil evenly moist. Mulch plants to help with this.

Blossom-End Rot
Blossom-end rot is caused by a calcium deficiency and can be prevented by spraying the foliage of young plants with calcium chloride. Once the rot shows up, it may be too late; if you notice blossom-end rot, remove diseased fruit immediately in hopes that upcoming fruit will develop as normal. Spray plants to prevent blossom-end rot if there's a history of this disease in your garden. Supplying even moisture helps prevent the disease. Mulching under tomato plants helps prevent early blight as it helps keep the soil evenly moist, reducing the likelihood of blossom-end rot.

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